The WORK-ENERGY THEOREM

Kinetic energy is expressed in joules just like work, since in the case we just looked at, W = K. In fact, the derivation above can be extended to an object with a nonzero initial speed, and the same analysis will show that the total work done on an object - or, equivalently, the work done by the net force - will equal its change in kinetic energy; this is known as the work-energy theorem:

Notice that kinetic energy, like work, is a scalar quantity.

Example:

1.) What is the kinetic energy of a baseball (mass = 0.15 kg) moving with a speed of 36 m/s?

Solution: 

From the definition,

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Test Yourself!!!

1.) A tennis ball (mass = 0.06 kg) is hit straight upward with an initial speed of 45m/s. How high would it go if air resistance were negligible?

2.) A pool cue striking a stationary billiard ball (mass = 0.25 kg) gives the ball a speed of 1.5 m/s. If the force of the cue on the ball was 20 N, over what distance did this force act?